1. Field of the Invention
The present invention relates to a wafer polishing apparatus having a measurement device and a polishing method using the apparatus for the fabrication of semiconductor devices. More particularly, the present invention relates to a wafer polishing apparatus having a measurement device for determining the polishing state of a wafer before cleaning the wafer, and the associated polishing method.
2. Description of the Related Art
The patterns formed on a semiconductor wafer are growing more and more intricate as semiconductor devices achieve greater functionality using highly miniaturized components in greater densities on the chip. Such devices utilize multi-layered circuit patterns to connect the individual components. Step-height differences between deposited layers of adjacent unit cells are reduced using Chemical Mechanical Polishing (CMP) techniques.
As shown in the schematic plan diagram in FIG. 1, the conventional CMP process is executed by performing a polishing process inside a polishing apparatus 10, performing a cleaning process inside a separate chemical cleaning apparatus 12, and then analyzing the polished state of the wafer inside a separate measurement apparatus 14.
A grinding surface is formed on the upper surface of a rotatable polishing table 16 inside the polishing apparatus 10. Nozzles (not shown), located a predetermined distance above the upper surface of the polishing table 16, spray a grinding solution, i.e., a slurry, onto the polishing table 16. Near the polishing table 16 is located a standby stage 18. The standby stage 18 is annular and is turned in equal increments. On the standby stage 18 are stands 22 and 24 for placing wafers on the standby stage 18. In the conventional polishing apparatus shown in FIG. 1 five pre-polishing stands 22 and five post-polishing stands 24 are alternately installed on the standby stage 18. Wafers to be polished are placed on the pre-polishing stands 22, and the polished wafers are placed on the post polishing stands 24 after completion of the polishing process.
In addition, a rinsing device 20 is included for rinsing the wafers using deionized water after the wafers are polished. The rinsing device is disposed inside the annulus of the standby stage 18.
On one side near the standby stage 18, there is a loading section which includes one or more loading platforms 28 for mounting one or more loading cassettes. A loading cassette holds a plurality of wafers to be polished. The side of each wafer to be polished is termed the front side. The loading section includes a loading robot arm 27 for transferring a wafer from a loading cassette on the loading platform 28 to a pre-polishing stand 22 of the standby stage 18. A wafer is placed upside down on a pre-polishing stand 22 such that the front side of the wafer contacts the surface of the pre-polishing stand 22.
On another side of the standby stage 18, there is a unloading section which includes an unloading robot arm 25 and one or more unloading platforms 26 for mounting one or more unloading cassettes. The unloading robot arm 25 transfers a wafer on the post-polishing stand 24 of the standby stage 18 to a specific position in an unloading cassette on an unloading platform 26.
In addition, a wafer moving device is positioned above the standby stage 18. As shown in FIG. 2, a wafer moving device 30 has a body 32 which is cylindrical and five spindles 34 connected to the body 32. Each spindle 34 has a wafer carrier 36 attached. The wafer moving device 30 is movable back and forth, and up and down. Each spindle 34 can be rotated about its own long axis, and can be translated from near the outside edge of the device body 32 cylinder radially to a position near the center of the device body 32 cylinder and back. That is, the spindles 34 are rotatable and radially reciprocating. A wafer is temporarily fixed to a wafer carrier 36 by applying suction to the back side of the wafer.
Inside a conventional chemical cleaning apparatus 12, there are a container (not shown) having a certain amount of chemicals and a dryer (not shown) for removing liquid collected on the wafers during the cleaning process. In using the conventional, separate cleaning apparatus 12, a cassette of wafers is transported to the chemical cleaner 12 after the polishing process.
After cleaning the wafers in the chemical cleaning apparatus 12, the wafers are transported to the separate measurement apparatus 14, and analyzed. In the measurement apparatus 14, the thickness of the outermost layer of the front side of the wafer is optically measured.
The operation of these conventional apparatuses is described next. In the polishing apparatus 10, five wafers of the plurality of wafers loaded in the loading cassette on the loading platform 28 are transferred front side down, one by one, to the pre-polishing stands 22 using a reciprocating movement of the loading robot arm 27. After each wafer is placed front side down on a pre-polishing stand 22, the standby stage 18 is turned an equal increment to bring the next pre-polishing stand into the operating range of the loading robot arm 27, i.e., into the work envelope of the loading robot arm 27.
Then, the wafer moving device 30 above the standby stage 18 descends, and the wafer carriers 36 of the wafer moving device 30 use suction to temporarily fix all five wafer carriers simultaneously to the back sides of the corresponding five wafers on the five pre-polishing stands 22. Then, the wafer moving device 30 moves upward, and then horizontally so as to be positioned above the polishing table 16 with all five wafers, front side down. The wafer moving device then again descends so that the surface of the polishing table 16 closely contacts the front surfaces of the wafers. Next, the polishing table 16 rotates while the spindles 34 simultaneously rotate and reciprocate radially. At the same time, a slurry grinding solution is sprayed on the upper surface of the polishing table 16 from the nozzles (not shown) above the polishing table 16. The grinding surface formed on the upper side of the polishing table 16 is brought into contact with the front surface of the wafers such that the front side of the wafer is polished by the chemical and physical (mechanical) mechanisms of the polishing process.
During the polishing process different pressures may be generated between the wafer and the grinding surface formed on the upper surface of the polishing table 16. The different pressures result in different thicknesses among the outermost layers of the different polished wafers. The thickness of the outermost layer is later analyzed in a measurement apparatus as described below.
After the polishing is completed according to a predetermined schedule, the wafer moving device 30 ascends and moves horizontally to carry the wafers to the rinsing device 20. There, the polished wafers are rinsed in de-ionized water. Then, the rinsed wafers are transferred to the five post-polishing stands 24 of the standby stage 18 by the wafer moving device 30.
The wafers on the post-polishing stands 24 of the standby stage 18 are loaded one by one onto an unloading cassette on an unloading platform 26 by the repeated, reciprocating movement of the unloading robot arm 25, and by the equal incremental turns of the standby stage 18 bringing the next post-processing stand into the work envelope of the unloading robot arm 25.
Then, the wafers in an unloading cassette on an unloading platform 26 are transported to the chemical cleaning apparatus 12 by an automatic transporting device (not shown), and those wafers are put into the container (not shown) inside the chemical cleaning apparatus 12 to be cleaned and then dried in a dryer (not shown).
The wafers passing through the chemical cleaning apparatus are finally transported into the measurement apparatus 14 for the analysis process to measure the thickness of the outermost layer of the front side of each polished wafer. Thereafter, if a polished wafer is found to have an abnormal thickness for the outermost layer, the wafer is again input into the the polishing apparatus 10 so as to go through the polishing process another time.
In addition to the normal polishing just described, the polishing apparatus also undergoes a calibration check. Before operating on wafers containing actual semiconductor devices, dummy wafers are loaded into the polishing apparatus 10. The dummy wafers then pass through the polishing process and the cleaning process. Then, the polishing apparatus is checked for malfunctions by carrying out the analysis process in the measurement apparatus 14. In the case that a malfunction of the polishing apparatus 10 is found, the operational conditions in the polishing apparatus 10 are readjusted. Hence the polishing apparatus is calibrated.
During both normal operations and calibration, wafers are removed from the polishing apparatus and cleaned before undergoing analysis in the measurement apparatus. Checking for abnormalities after performing the cleaning process causes a loss of time. However, if the analysis process were performed right after the polishing process inside the polishing apparatus without cleaning first, the abnormal polishing could be detected and corrected earlier, thus saving time. Also, since the conventional polishing apparatus, chemical cleaning apparatus, and measurement apparatus are separate, a loss of time is caused during transportation of the wafers between these apparatuses. That is, extra time is required to transport the wafers from the polishing apparatus to the chemical cleaning apparatus, and from the chemical cleaning apparatus to the measurement apparatus.
Similarly, when the polishing apparatus is calibrated with the dummy wafers using the conventional apparatuses, the dummy wafers are measured after the cleaning process inside the chemical cleaning apparatus, thereby causing a loss of time. If calibration is also performed by passing wafers immediately into the measurement apparatus, skipping the cleaning process, a great savings of time can be achieved.
Therefore what is needed is a polishing apparatus that will perform measurements on the outermost layer of the front side of a wafer, or calibration to detect and correct malfunctions, before cleaning in a chemical cleaning device. Also needed is a polishing device that is not separate from a cleaning device and a measurement device, to avoid delays incurred as wafers are transported among separate devices.